Speciation of copper in ZSM-48 during NO reduction

Speciation of copper in ZSM-48 and MCM-41 was studied by in situ extended X-ray absorption fine structural (EXAFS) and X-ray absorption near edge structural (XANES) spectroscopies to reveal the abrupt changes in yields of N₂O, NO₂ and CO₂ from the catalytic reduction of NO with CO at 673 K. Component fitted XANES spectra showed that oxygen was inserted into the metallic copper (Cu(0)) in ZSM-48 and MCM-41 during NO reduction. In the confined channels of ZSM-48, about 91% of total copper was Cu(I) that involved in the catalytic reduction of NO with CO at 673 K. By in situ EXAFS, we found that during the NO reduction process, the oxygen-inserted copper possessed Cu-O, Cu-Cu, and Cu-(O)-Cu bond distances of 1.88, 2.61 and 2.95 Å, respectively, suggesting the possible existence of a linear type cluster with an averaged structure of Cu₂O in ZSM-48. Furthermore, in the channels of ZSM-48, due to the restricted diffusion, NO reduction as well as CO oxidation might primarily occur at the head or end of the clusters. Note that NO could penetrate into ZSM-48 containing the clusters. On the contrary, in the parallel experiment, mainly CuO was observed in the mesopores (∼32 Å) of MCM-41.